1. Field
This disclosure relates to the field of communication technologies, and in particular to an apparatus and method for estimating a frequency offset, an apparatus and method for estimating a channel spacing and a system.
2. Description of the Related Art
In an optical fiber communication system, carrier data are modulated in optical carriers. Under an ideal condition, wavelengths of lasers are stable, hence, carrier wavelengths are constant. However, in a practical system, as wavelengths of lasers are influenced by factors such as variation of driving currents, temperature fluctuation, and resonant cavity aging, etc., output carrier wavelengths drift in a certain range, embodied as frequency offsets of the carriers (frequency offsets). Such indefinite variation of frequency offsets will bring relatively large influence to the optical communication system, which is mainly embodied as: 1) making demodulation of the carrier data difficult; and 2) possibly introducing neighboring channel crosstalk into the multicarrier system. An effective method for estimating a frequency offset is effective means for solving the inherent frequency offset problem of the system.
Currently, a training sequence plays an important role in a high-speed optical fiber communication system. First, as optical fiber channels are not ideal, it is often needed to introduce a training sequence to assist the receiver in performing channel equalization. And what is more important is that the training sequence may further be used to assist in performing frequency offset estimation and compensation, so as to eliminate influence of inherent frequency offsets. In view of the important role of the training sequence in resisting the frequency offsets, an effective training sequence design and a frequency offset estimation method become keys in improving a performance of the transmission system. Under a nonideal condition, system noise is a key factor influencing the performance of frequency offset estimation of the training sequence, an effective training sequence design and a processing method may enhance anti-noise characteristic of the training sequence, and improvement of the anti-noise characteristic is not only beneficial to the frequency offset estimation, but also brings about enhancement of several functions of the training sequence, so that the whole system has a good communication performance.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the disclosure.